This invention relates generally to gas turbine engines and more particularly, to prebooster and precompressor water injection in a gas turbine engine.
Gas turbine engines typically include a compressor for compressing a working fluid, such as air. The compressed air is injected into a combustor which heats the fluid causing it to expand, and the expanded fluid is forced through a turbine. The compressor typically includes a low pressure compressor and a high pressure compressor.
The output of known gas turbine engines may be limited by the temperature of the working fluid at the output of the high pressure compressor, sometimes referred to as temperature xe2x80x9cT3xe2x80x9d, and by the temperature of the working fluid in the combustor outlet, sometimes referred to as temperature xe2x80x9cT41xe2x80x9d. To reduce both the T3 and T41 temperatures, at least some known engines use an intercooler positioned in the fluid flow path between the low pressure compressor and the high pressure compressor. In steady state operation, the intercooler extracts heat from the air compressed in the low pressure compressor, which reduces both the temperature and volume of air entering the high pressure compressor. Such reduction in temperature reduces both the T3 and T41 temperatures. Increased power output therefore can be achieved by increasing flow through the compressor. However, such an intercooler may also reduce thermal efficiency of the engine.
To facilitate reducing both the T3 and T41 temperatures for power augmentation, without sacrificing engine thermal efficiency, at least some known engines include prebooster or precompressor water injection. The water spray facilitates reducing both the T3 and T41 temperatures, and also reduces compressive engine horsepower. Because the T3 and T41 temperatures are reduced, the engine is not T3 and T41 constrained, the engine may operate at higher output levels below the T3 and T41 temperature limits.
In one aspect, a method for operating a gas turbine engine including a high pressure compressor and a water injection apparatus for injecting water into a flow of the engine upstream from the high pressure compressor is provided. The method includes the steps of operating the engine without injecting water into the gas flow of the engine, injecting water at a first flow rate into the gas flow for power augmentation once engine full power is about reached, and injecting water into the engine at an increased second flow rate for evaporative cooling of engine components downstream from the high pressure compressor.
In another aspect of the invention, a method for operating a gas turbine engine is provided. The method includes the steps of injecting water into the gas flow at a first flow rate for power augmentation once engine full power is about reached, accelerating the engine to full power while water is injected at the first flow rate, and injecting water at a second flow rate into the engine for evaporative cooling of engine components while the engine is maintained at a substantially constant operating power.
In a further aspect, a method for operating an engine including a high pressure compressor and a water injection system including a plurality of nozzles is provided. The method includes the steps of operating the engine at full power without injecting water into the gas flow of the engine, injecting water through the nozzles into the gas flow at a first flow rate for power augmentation once engine full power is about reached, accelerating the engine to full power while water is injected at the first flow rate, and injecting water at a second flow rate through the nozzles into the engine for evaporative cooling of engine components while the engine is maintained at a substantially constant operating power, wherein the second flow rate is at least approximately five percent greater than a corresponding water injection first flow rate used for power augmentation.